The invention relates to a disc brake for a commercial vehicle. The disc brake includes a caliper that straddles a brake disc and has two brake linings (pads) arranged one on each side of the brake disc. The disc brake is equipped with an adjustment device for compensating wear of the brake linings. The adjustment device has at least one adjustment spindle or piston associated with a slip clutch, which is actuated when a given torque is exceeded.
A brake of this type is known from EP 05 66 008 A1.
The vehicle brake in question is designed, in particular, for commercial vehicles. Especially in these vehicles, the brake linings are highly stressed because of the large masses to be braked. The wear of the brake linings is therefore correspondingly high. The adjustment device is so designed that adjustment takes place according to the degree of wear of the brake linings.
When brake linings are exchanged, it can occur, because of the design of the adjustment device, that a permissible torque of the internal adjustment mechanism is exceeded. This torque is applied via a manual readjustment device, or the adjustment spindle. If a given torque is exceeded in this way, the slip clutch is actuated. This clutch might also be referred to as a safety or overload clutch. In the case of the disc brake in question here, the slip clutch has the function of preventing damage or destruction caused by the shortcomings of the adjustment device.
Slip clutches are generally known. Friction clutches with a constant application force, which force may, however, also be adjustable, are distinguished in terms of function. So-called multi-disc clutches having a different construction are also used. The discs are made either of steel, although they may also be provided with friction linings. The application force is generated by suitable springs.
It is the object of the present invention to configure a disc brake of the type described in detail above in such a manner that the slip clutch can be manufactured at low cost and can be designed in accordance with the installation possibilities existing in disc brakes.
This object is achieved by configuring the slip clutch in the manner of a safety adapter, which is mounted on an end region of each adjustment spindle by a non-positive connection such that the safety adapter can be rotated with respect to the adjustment spindle when a given torque is exceeded.
In the normal embodiment of the disc brake, the adjustment device is designed such that it is equipped with two adjustment spindles running parallel to and at a distance from one another. The adjustment spindles are connected drivingly to one another via a synchronization device. Consequently, the safety adapter is mounted on the end region of each adjustment spindle oriented away from the synchronization device.
The safety adapter is an extremely simple component, which is configured in the manner of a sleeve and can be produced with the necessary precision by means of a suitable manufacturing process. The magnitude of the forces forming the non-positive connection is governed by the torque which must be transmitted in the normal operating state of the brake.
According to a preferred embodiment, it is provided that the non-positive connection between the adjustment spindle and the safety adapter is formed by a press fit. This press fit may be effected in various ways.
For example, it is provided that the external diameter of the adjustment spindle has, at least in the region of the safety adapter, an oversize with respect to the internal diameter of the safety adapter, and/or that the internal diameter of the safety adapter has an oversize with respect to the external diameter of the adjustment spindle. Independently of the oversize, however, the safety adapter is expanded when it is pressed onto the end region of the adjustment spindle, since the safety adapter is in the form of a sleeve at least in the region over which the end region of the adjustment spindle extends, while the end region of the adjustment spindle is solid. In the possibilities described previously, however, the external diameter of the adjustment spindle and the internal diameter of the safety adapter have a circular configuration.
According to a further embodiment, it is provided that the press fit between the end region of the adjustment spindle and the safety adapter is formed by an external contour of the adjustment spindle and/or an internal contour of the safety adapter, which contour deviates from a circular one.
This embodiment has the advantage that an elastic deformation of the safety adapter and/or of the end region of the adjustment spindle takes place as the safety adapter is pressed onto the end region of the adjustment spindle, so that the non-positive connection is especially intimate. If the end region of the adjustment spindle is circular, the safety adapter is deformed to a circular contour as it is pressed on. Because, with this method, the compressive forces are not produced solely by expansion of the safety adapter, but rather bending stresses also occur as a result of the deformation of the contour of the safety adapter, the end region of the adjustment spindle can have a relatively large oversize, yielding the advantage that the tolerances can be larger.
In another preferred embodiment, the safety adapter is made from an especially ductile and tough material. If the end region of the adjustment spindle is oversized with respect to the bore of the safety adapter, a plastic deformation of the safety adapter takes place; that is, during the pressing-on process, the bore diameter is permanently enlarged through adaptation to the actual diameter of the end region of the adjustment spindle, determining a residual tension force in the press-fit connection. This residual tension force is determined by the yielding point of the material selected for the safety adapter.
In a further development, it is provided that, in relation to the separated state of the adapter from the end region of the adjustment spindle, the external contour of the end region of the adjustment spindle, and/or the internal contour of the safety adapter, is/are configured in the manner of a polygon. In a preferred embodiment, this polygon is an oval, an ellipse or a triangular or quadrangular polygon, the deviations from the circular shape being relatively small.
Because, in a preferred embodiment, the safety adapter is deformed as it is pressed onto the end region of the adjustment spindle, it is provided that the safety adapter is in the form of a sheet-metal press part produced by a deep-drawing process. However, in another embodiment, it is also possible for the safety adapter to be configured as a press part produced by cold forming. This press part might be produced, for example, by means of a suitable tool. Furthermore, the safety adapter might be a molded part produced by a sintering process.
In order that the adjustment device can still be readjusted in the event of damage to or loss of the adapter, it is provided that the end region of the adjustment spindle associated with the safety adapter is provided with a polygonal recess, preferably a hexagon socket.
The safety adapter is configured in such a manner that it projects with respect to the end face of the adjustment spindle and that the projecting portion has, at least over a certain length, a polygonal configuration, preferably in the form of a hexagon key.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.